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From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Daniel Wang <wonderfly@google.com>
Cc: sergey.senozhatsky.work@gmail.com, Petr Mladek <pmladek@suse.com>,
	rostedt@goodmis.org, stable@vger.kernel.org,
	Alexander.Levin@microsoft.com, akpm@linux-foundation.org,
	byungchul.park@lge.com, dave.hansen@intel.com,
	hannes@cmpxchg.org, jack@suse.cz, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Mel Gorman <mgorman@suse.de>,
	mhocko@kernel.org, pavel@ucw.cz,
	penguin-kernel@i-love.sakura.ne.jp, peterz@infradead.org,
	tj@kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz,
	Cong Wang <xiyou.wangcong@gmail.com>,
	Peter Feiner <pfeiner@google.com>
Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes"
Date: Mon, 22 Oct 2018 19:09:52 +0900	[thread overview]
Message-ID: <20181022100952.GA1147@jagdpanzerIV> (raw)
In-Reply-To: <CAJmjG2-e6f6p=pE5uDECMc=W=81SYyGCmoabrC1ePXwL5DFdSw@mail.gmail.com>

On (10/21/18 11:09), Daniel Wang wrote:
> 
> Just got back from vacation. Thanks for the continued discussion. Just so
> I understand the current state. Looks like we've got a pretty good explanation
> of what's going on (though not completely sure), and backporting Steven's
> patches is still the way to go?

Up to -stable maintainers.

Note, with or without Steven's patch, the non-reentrable consoles are
still non-reentrable, so the deadlock is still there:

	spin_lock_irqsave(&port->lock, flags)
	 <NMI>
	  panic()
	   console_flush_on_panic()
	    spin_lock_irqsave(&port->lock, flags)		// deadlock


// And I wouldn't mind to have more reviews/testing on [1].


Another deadlock scenario could be the following one:

	printk()
	 console_trylock()
	  down_trylock()
	   raw_spin_lock_irqsave(&sem->lock, flags)
	    <NMI>
	     panic()
	      console_flush_on_panic()
	       console_trylock()
	        raw_spin_lock_irqsave(&sem->lock, flags)	// deadlock

There are no patches addressing this one at the moment. And it's
unclear if you are hitting this scenario.


> I see that Sergey had sent an RFC series for similar things. Are those
> trying to solve the deadlock problem in a different way?

Umm, I wouldn't call it "another way". It turns non-reentrant serial
consoles to re-entrable ones. Did you test patch [1] from that series
on you environment, by the way?

[1] lkml.kernel.org/r/20181016050428.17966-2-sergey.senozhatsky@gmail.com

	-ss

  parent reply	other threads:[~2018-10-22 10:10 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-27 19:46 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes" Daniel Wang
2018-10-01 19:23 ` Steven Rostedt
2018-10-01 20:13   ` Pavel Machek
2018-10-01 20:21     ` Vlastimil Babka
2018-10-01 20:38       ` Daniel Wang
2018-10-01 20:29     ` Steven Rostedt
2018-10-01 20:37   ` Daniel Wang
2018-10-01 20:40     ` Sasha Levin
2018-10-02  8:42     ` Petr Mladek
2018-10-02 17:21       ` Daniel Wang
2018-10-03  0:15       ` Daniel Wang
2018-10-03  1:23         ` Steven Rostedt
2018-10-03  9:14           ` Petr Mladek
2018-10-03 17:16             ` Daniel Wang
2018-10-03 17:37               ` Steven Rostedt
2018-10-03 18:37                 ` Daniel Wang
2018-10-03 23:37                   ` Daniel Wang
2018-10-04  7:44                   ` Sergey Senozhatsky
2018-10-04  8:05                     ` Sergey Senozhatsky
2018-10-04  8:36                     ` Petr Mladek
2018-10-04  8:55                       ` Sergey Senozhatsky
2018-10-21 18:09                         ` Daniel Wang
2018-10-22  9:32                           ` Petr Mladek
2018-10-22 10:09                           ` Sergey Senozhatsky [this message]
2018-11-01 16:05                             ` Daniel Wang
2018-11-09  6:47                               ` Sergey Senozhatsky
2018-12-12  1:16                                 ` Daniel Wang
2018-12-12  5:21                                   ` Sergey Senozhatsky
2018-12-12  6:08                                     ` Daniel Wang
2018-12-12  6:28                                       ` Sergey Senozhatsky
2018-12-12  6:48                                         ` Sasha Levin
2018-12-12  8:10                                           ` Sergey Senozhatsky
2018-12-12 13:36                                             ` Petr Mladek
2018-12-12 13:59                                               ` Sergey Senozhatsky
2018-12-12 17:43                                                 ` Sasha Levin
2018-12-12 20:11                                                   ` Daniel Wang
2018-12-12 21:43                                                     ` Sasha Levin
2018-12-12 21:49                                                       ` Daniel Wang
2018-12-12 21:52                                                         ` Sasha Levin
2018-12-12 21:56                                                           ` Daniel Wang
2018-12-13  0:40                                                             ` Daniel Wang
2018-12-13  2:27                                                               ` Sergey Senozhatsky
2018-12-13  2:39                                                                 ` Daniel Wang
2018-12-13  9:59                                                                   ` Petr Mladek
2018-12-13 14:29                                                                     ` Sasha Levin
2018-12-13  2:07                                                           ` Sergey Senozhatsky
2018-12-28  0:16                                             ` Sergey Senozhatsky
2018-12-28  8:27                                               ` Greg KH
2018-12-28 22:03                                                 ` Daniel Wang
2018-12-30  3:03                                                   ` Sergey Senozhatsky
2018-10-04  7:49                 ` Petr Mladek
2018-10-02  8:16 ` Sergey Senozhatsky

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